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HOME   About AusCERT   Membership   Contact Us   PKI Services   Training   Publications   Sec. Bulletins   Conferences   News & Media   Services   Web Log   Site Map   Site Help   Member login Login »  Become a member »   Home » Security Bul... » AA-97.19 -- SGI IRIX df Buffer Overrun Vulnerability   AA-97.19 -- SGI IRIX df Buffer Overrun Vulnerability Date: 17 December 1997 Click here for printable version -----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AA-97.19 AUSCERT Advisory SGI IRIX df Buffer Overrun Vulnerability 26 May 1997 Last Revised: 17 December 1997 Changed Section 3 to include vendor patch and bulletin information. A complete revision history is at the end of this file. - --------------------------------------------------------------------------- AUSCERT has received information that a vulnerability exists in df(1), distributed under IRIX versions 5.x and 6.x. Other IRIX versions may also be vulnerable. This vulnerability may allow local users to gain root privileges. Exploit information involving this vulnerability has been made publicly available. Vendor patches have been released addressing this vulnerability. AUSCERT recommends that sites take the steps outlined in section 3 as soon as possible. This advisory will be updated as more information becomes available. - --------------------------------------------------------------------------- 1. Description df(1) is a program used to display statistics about the amount of used and free disc space on file systems. Due to insufficient bounds checking on arguments which are supplied by users, it is possible to overwrite the internal stack space of the df program while it is executing. By supplying a carefully designed argument to the df program, intruders may be able to force df to execute arbitrary commands. As df is setuid root, this may allow intruders to run arbitrary commands with root privileges. Sites can determine if this program is installed by using: % ls -l /sbin/df df is installed by default in /sbin. Sites are encouraged to check for the presence of this program regardless of the version of IRIX installed. Specific versions of IRIX which are vulnerable to this problem are listed in Section 3.3. Exploit information involving this vulnerability has been made publicly available. 2. Impact Local users may gain root privileges. 3. Workarounds/Solution Official vendor patches have been released by Silicon Graphics which address this vulnerability (Section 3.3). If the patches recommended by Silicon Graphics cannot be applied, AUSCERT recommends that sites prevent the exploitation of this vulnerability by immediately applying the workaround given in Section 3.1. If the df functionality is required by non-root users and patches can not be installed, AUSCERT recommends applying the workaround given in Section 3.2. 3.1 Remove setuid and non-root execute permissions To prevent the exploitation of the vulnerability described in this advisory, AUSCERT recommends that the setuid permissions be removed from the df program immediately. As df will no longer work for non-root users, it is recommended that the execute permissions for them also be removed. # ls -l /sbin/df -r-sr-xr-x 1 root sys 23136 Nov 22 1994 /sbin/df # chmod 500 /sbin/df # ls -l /sbin/df -r-x------ 1 root sys 23136 Nov 22 1994 /sbin/df 3.2 Install df wrapper AUSCERT has developed a wrapper to help prevent programs from being exploited using the vulnerability described in this advisory. Sites which have a C compiler can obtain the source, compile and install the wrapper. The source for the wrapper, including installation instructions, can be found at: ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/ overflow_wrapper.c This wrapper replaces the df program and checks the length of the command line arguments which are passed to it. If an argument exceeds a certain predefined value (MAXARGLEN), the wrapper exits without executing the df command. The wrapper program can also be configured to syslog any failed attempts to execute df with arguments exceeding MAXARGLEN. For further instructions on using this wrapper, please read the comments at the top of overflow_wrapper.c. When compiling overflow_wrapper.c for use with df, AUSCERT recommends defining MAXARGLEN to be 32. The MD5 checksum for the current version of overflow_wrapper.c can be retrieved from: ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/CHECKSUM The CHECKSUM file has been digitally signed using the AUSCERT PGP key. 3.3 Install vendor patches Silicon Graphics has released a security bulletin containing information on this vulnerability including patch details. The original release of this bulletin can be retrieved from: ftp://sgigate.sgi.com/security/19970505-02-PX Information on patches which address the vulnerability described in this advisory has been extracted from the SGI bulletin and is listed below. OS Version Vulnerable? Patch # Other Actions ---------- ----------- ------- ------------- IRIX 3.x unknown not avail Note 1 IRIX 4.x unknown not avail Note 1 IRIX 5.0.x yes not avail Note 1 IRIX 5.1.x yes not avail Note 1 IRIX 5.2 yes not avail Note 1 IRIX 5.3 yes 2224 IRIX 6.0.x yes not avail Note 1 IRIX 6.1 yes not avail Note 1 IRIX 6.2 yes 2177 IRIX 6.3 yes 2232 IRIX 6.4 yes 2233 NOTES 1) upgrade operating system or see "Temporary Solution" section. "Temporary Solution" refers to the SGI bulletin but is equivalent to the suggestions given in our AUSCERT advisory in section 3.1. These patches can be retrieved from: http://www.sgi.com/Support/Secur/security.html - --------------------------------------------------------------------------- The AUSCERT team have made every effort to ensure that the information contained in this document is accurate. However, the decision to use the information described is the responsibility of each user or organisation. The appropriateness of this document for an organisation or individual system should be considered before application in conjunction with local policies and procedures. AUSCERT takes no responsibility for the consequences of applying the contents of this document. If you believe that your system has been compromised, contact AUSCERT or your representative in FIRST (Forum of Incident Response and Security Teams). AUSCERT is located at The University of Queensland within the Prentice Centre. AUSCERT is a full member of the Forum of Incident Response and Security Teams (FIRST). AUSCERT maintains an anonymous FTP service which is found on: ftp://ftp.auscert.org.au/pub/. This archive contains past SERT and AUSCERT Advisories, and other computer security information. AUSCERT also maintains a World Wide Web service which is found on: http://www.auscert.org.au/. Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 4477 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AUSCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for emergencies. Postal: Australian Computer Emergency Response Team Prentice Centre Brisbane Qld. 4072. AUSTRALIA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Revision History 17 Dec 1997 Silicon Graphics has released a security bulletin addressing the vulnerability described in this advisory. Section 3 has been modified to include vendor patch information. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBNJfY6Ch9+71yA2DNAQGAUwP9Fghb3FJAix51VrHyXEvtRqnAmF89wbD0 eb6xBonVCnvY3zxQBfUXmHlCHXhtSUtqaHE4gsCbR0i+EZtlvZSy+fFdCMcgfc/J 1nsUD2tg1ElOxsqvJP48wHGoVbfv++KFkxGCOSXGCxPOlh9wDnXf46AIa3lbtFft rtCGapZyH+8= =LKex -----END PGP SIGNATURE-----

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